This invention relates to a novel resist material which is sensitive to electron-beams, X-rays, deep ultraviolet rays and near ultraviolet rays and highly resistive to dry etching, and to a pattern forming method in which the novel resist material is used to form a resist pattern that serves as a mask for dry etching of an underlying organic layer.
In the manufacture of microelectronic devices such as semiconductor integrated circuit devices including LSI devices and bubble memory devices, optical lithography and electron-beam lithography are widely used to form fine patterns. The thickness of a resist layer is an important factor in realization of high resolution patterns. It is well known that the use of a thick resist layer results in low resolution mainly by reason of reflection from the substrate in the case of optical lithography and scattering of electrons in the case of electron-beam lithography.
Recently, dry etching techniques such as gas plasma etching, reactive sputter etching and ion milling are often used for the purpose of transferring a resist pattern produced by exposure and development into the substrate with high accuracy. In such cases, it is difficult to use a desirably thin resist layer to thereby obtain a high resolution pattern because the resist pattern too undergoes etching during the dry etching process and fails to exhibit resistivity sufficient for processing of the substrate. Furthermore, it is not seldom that the surface of the substrate to be etched has steps, and in such cases it is necessary to form a considerably thick resist layer so as to accomplish complete coverage of the steps to thereby provide a flat surface. Then, it becomes very difficult to form fine patterns in such a thick resist layer.
To solve the above described problems, J. M. Moran et al have proposed a three-layer technique in Journal of Vacuum Science and Technology, Vol. 16, No. 6, 1620 (1979). According to this three-layer technique the first layer which covers the substrate surface and provides a flat surface is a sufficiently thick layer of an organic material such as a conventional resist material, and the intermediate layer is formed of an inorganic material that cannot easily be etched by dry etching with oxygen, such as silicon, silicon dioxide or silicon nitride. The third or top layer is a thin resist layer. In the patterning process, first the resist layer is exposed to light, X-ray or electron-beams and developed to produce a resist pattern. Next, the intermediate layer is subjected to dry etching with the resist pattern as a mask. Finally, the thick organic layer is etched by reactive sputter etching using O.sub.2 with the patterned intermediate layer as a mask. By this method a high resolution pattern initially generated in the thin resist layer can be transferred to the thick organic layer which is in direct contact with the substrate surface. However, it is a disadvantage of the three-layer technique that the processing operations become complicated and time-consuming mainly because of the addition of the intermediate layer which is formed by vacuum deposition, sputtering or plasma CVD method.
If it is practicable to use a resist material which is sufficiently resistive to dry etching, it becomes possible to etch a thick organic layer by directly using the initially patterned resist layer as a mask, so that the above described three-layer structure can be simplified to a two-layer structure. To our knowledge, however, such a convenient resist material is not available in the present state of the art. Polydimethylsiloxane is known as resistive to dry etching to such extent that the etch rate of this material by O.sub.2 plasma etching is nearly zero. However, polydimethylsiloxane is unsuitable for practical use as a resist material because this polymer is liquid at room temperature so that a coating film of this polymer is liable to suffer from adhesion of dust particles and fail to provide a high resolution pattern due to its fluidity.
In our co-pending application Serial No. 501,201 filed June 6, 1983, we have proposed a pattern forming method of the two-layer type using a resist meterial which comprises a polymer or copolymer having trialkylsilyl, trialkoxysilyl or dimethylphenylsilyl groups. This resist material is highly resistive to reactive sputter etching with O.sub.2 and sensitive to electron beams and deep ultraviolet rays, but this resist material does not undergo cross-linking by exposure to visible light or near ultraviolet rays and, hence, cannot be used as a photoresist.